Chemical equilibrium removing products/adding reactants

What happens to a system at equilibrium if the concentration of one of the reacting chemicals is changed This question has practical importance, because many manufacturing processes are continual. Products are removed and more reactants are added without stopping the process. For example, consider the Haber process that was mentioned in the previous Sample Problem. 

In our above chemical demonstration, we also had a dynamic, reversible situation copper carbonate precipitate formed, but it also redissolved. When we added vinegar, we removed some of the carbonate from the equilibrium. The solid redissolved in an effort to reestablish equilibrium concentrations of both reactant and product. 

In ERD in situ separation is used to improve the yield of reaction whereas an entrainer feed is added to make the separation feasible by selectively increasing the relative volatility of one of the products, ERD promises to be advantageous for the synthesis of fatty acid esters. The entrainer increases the relative volatility of water (by-product) compared to the alcohol (reactant), such that during the reaction the water can be continuously removed by distillation. In this way the chemical equilibrium is shifted such that higher conversions can be obtained. In Figure 1 the flowsheet of the desired process is given, in which RS stands for Reactive Section and DS for Distillation Section. 

Some chemical systems are reversible that is, they do not go to completion. Instead, they reach a point of equilibrium in which a certain ratio of the concentrations of the products to the concentrations of the reactants is constant. If more reactant particles are added to the system, the equilibrium is disturbed and the system responds by making more products, thus restoring the equilibrium ratio. Similarly, if reactant particles are removed, the products react in the reverse reaction to reform reactant particles and restore equilibrium. If the reactants and products have different colors, shifts in equilibrium can be followed by observing color changes as the system is disturbed. 

In this section we use Le ChateUer s principle to make qualitative predictions about how a system at equilibrium responds to various changes in external conditions. We consider three ways in which a chemical equilibrium can be disturbed (1) adding or removing a reactant or product, (2) changing the pressure by changing the volume, and (3) changing the temperature. 

Le Chatelier s principle states that a change in the conditions of a chemical system at equilibrium alters the concentrations of reactants and products, and a new equilibrium results. For example, if more reactant is added to a reaction at equilibrium, the concentrations of both reactants and products change to reestablish the equilibrium, and the equilibrium constant remains unchanged. After adding reactant, the total concentration of reactant initially increases, but then it decreases to establish a new equilibrium concentration. As a result, the concentration of the product increases. In short, the change imposed on the system by adding reactant is offset when some of the added reactant is converted to product. If a product is removed from a chemical system at equilibrium, the forward reaction occurs to give more product. We saw above the equilibrium constant for the formation of ethyl ethanoate from ethanoic acid and ethanol is 4.0. What if we would like to obtain a quantitative yield of product We can achieve this in two ways ... 

According to Le Chatelier s principle, if a chemical system at equilibrium is disturbed by adding a gaseous species (reactant or product), the reaction will proceed in such a direction as to consume part of the added species. Conversely, if a gaseous species is removed, die... 

If a chemical reaction is at equilibrium, Le Chatelier s principle predicts that adding a substance—either a reactant or a product—will shift the reaction so a new equilibrium is established by consuming some of the added substance. Removing a substance will cause the reaction to move in the direction that forms more of that substance. 

In industry, esterifications represent an important class of chemical reactions. As esterifications are equilibrium reactions (9), high yields can be obtained by adding an excess of one reactant or by constant removal of the produced water from the reaction mixture in order to shift the reaction to the product side. 

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